To Turn "Share On Facebook" Buttons ON
If you have turned the social sharing buttons off, you can turn them back on again. From the Privacy & Sharing page in the Host Control Panel, check the box next to the page or pages where you want to display the social sharing buttons. Then scroll to the bottom of the page and click the “Update Settings” submit button.
This setting is also available on the individual "page managers" for the pages where the Share on Facebook button appears.